1. Field of the Invention
The present invention relates to electromagnetic wave absorbing devices of flat lattice type suitable to cover a ceiling, sidewalls and a floor to construct a perfect electromagnetical non-echo room.
2. Prior Art
One of the known electromagnetic wave absorbing devices is shown in FIG. 12 and comprises a plurality of ferrite tiles 21 arranged in a matrix to cover electrically shielding sidewalls 22 of a housing. However, ferrite tile cannot suppress completely the reflection of incident electromagnetic wave at the surface of the tile. Moreover, the range of wavelength to be absorbed is limited due to the specific characteristics of ferrite.
Another of the known electromagnetic wave absorbing devices is shown in FIG. 13 and comprises a plurality of pyramid blocks 23, each having a square base, and being arranged in a matrix to cover an electrically shielding sidewall 22 of a housing. Each block 23 is composed of plastic foam containing carbon black powder and is attached to the shielding inner wall of the housing by means of electro-conductive adhesive to form the matrix of pyramids. Accordingly, there are large spaces between adjacent pyramids to reduce the absorption efficiency. Each pyramid body is needed to have a height from 70 cm to 100 cm to obtain a sufficient absorption rate. Moreover, when each pyramid is attached to the sidewalls to extend horizontally, the tip end portion of the pyramid tends to deform due to its own weight. The pyramid, bodies also occupy a considerable peripheral space of the room thereby reducing the effective center space of the electromagnetical non-echo room, or electromagnetical black room.